I disagree, this is not a duplicate of any of the mentioned questions. Those question asks about general disk space on the device, while the question is specific about using the Photo Library (as opposed to the documents folder for the app). For more see my answer.
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Ron SrebroNov 13 '11 at 18:03

Are there good news with the PhotosFramework for iOS 8? Can we do this check prior to save?
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PichirichiDec 25 '14 at 8:56

If you want some additional checks before, you can use the method mentioned in the comments to find the available disk space on the device, but there's no guarantee AssetLibrary doesn't use different logic to calculate disk space requirements.